High frequency switch

ABSTRACT

To provide a high frequency switch capable of dealing with multiple frequency bands without having plurality of switch circuits. A first diode that conducts due to a bias current when a first switch is closed is interposed between a first signal terminal and a second signal terminal. A strip line with the electrical length L 1  is connected to the cathode of the first diode, the other end being grounded. At a position with the distance L 2  from one end of the strip line, a capacitor and a second switch are connected to be equivalently grounded when a second switch is closed. The strip line resonates with the electrical length L 1  when the second switch is opened, and resonates with the electrical length L 2  when the second switch is closed.

TECHNICAL FIELD

The present invention relates to a high frequency switch, and moreparticularly to a high frequency switch for switching the signal path ina high frequency circuit for the mobile communication units.

BACKGROUND ART

A high frequency switch is employed for controlling the connectionbetween sending circuit and antenna, controlling the connection betweenreceiving circuit and antenna, and switching the signal path of highfrequency circuit in a mobile communication device such as a portabletelephone, a pager and a radio apparatus for business.

The conventional high frequency switch has the capacitors 62, 64 and adiode 63 connected in series between the signal terminals 61 and 65, asshown in FIG. 8. An inductor 66 is connected to the anode of the diode63, the other end of the inductor 66 being grounded via a capacitor 67.Moreover, a switch 68 is connected at an intermediate point between theinductor 66 and the capacitor 67, the other end of the switch 68 beingconnected via a resistor 69 to a power supply terminal 70. Also, thecathode of the diode 63 is connected to a strip line 71 with one endgrounded.

Herein, the electric length of the strip line 71 corresponds to aquarter wavelength of a high frequency signal used. Also, the inductor66 has an impedance to be large enough for the high frequency signal ina frequency band used. Moreover, the capacitors 62, 64 are couplingcapacitors for cutting DC components of the bias current, and thecapacitor 67 is a bypass capacitor for preventing high frequency signalfrom leaking into the power supply terminal 70.

In the above constitution, if the switch 68 is closed, an electriccurrent supplied from the power supply terminal 70 flows via theresistor 69 to the inductor 66, the diode 63, and the strip line 71.Thereby, the diode 63 conducts in a forward direction bias, enabling thehigh frequency signal to be transferred between the signal terminals 61and 65. At this time, the high frequency signal resonates in the stripline 71 grounded, so that the impedance as seen from the diode 63becomes infinite, whereby the high frequency signal is transferredwithout loss. On the other hand, if the switch 68 is opened, the diode63 is in a reverse direction bias to flow no current in a cut-off state,whereby the high frequency signal is not transferred between the signalterminals 61 and 65.

In this manner, the circuit of FIG. 8 controls the high frequency signalto conduct between the signal terminals 61 and 65 by opening or closingthe switch 68, and functions as a high frequency switch.

In the recent mobile communication device, the communication systems indifferent frequency bands coexist along with the increasing number ofusers and the diversification of functions in frequency band in aspecific communication system or at a specific location. To allow onemobile communication device to deal with a plurality of communicationsystems in different frequency bands, a high frequency switch usable indifferent frequency bands is required for its sending/receiving circuit.

However, in the high frequency switch with the conventionalconstitution, because only one usable frequency band is limitativelydecided by the electrical length of the strip line, it is necessary toprepare the high frequency switch different for every frequency band toallow one mobile communication device to deal with a plurality ofcommunication systems, resulting in a problem that the circuit becomescomplex and a large size.

The present invention has been achieved in the light of theabove-mentioned problems, and it is an object of the invention toprovide a high frequency switch capable of coping with a plurality offrequency bands without increasing the circuit scale by providing aplurality of switches.

SUMMARY OF THE INVENTION

The present invention firstly provides a high frequency switchcharacterized by comprising first switch means provided in a transitpath of high frequency signals to conduct by application of a DC bias, astrip line that resonates with a first high frequency signal in apredetermined frequency band to be supplied in the transit path of saidhigh frequency signal, with one end connected to said first switchmeans, and the other end grounded, and second switch means for switchingto resonate with a second high frequency signal in the predeterminedfrequency band by conducting by application of a DC bias toshort-circuit a part of said strip line, said second switch meansconnected in a halfway portion of said strip line. Secondly, theinvention provides the high frequency switch, characterized in that asecond strip line for resonating with said first high frequency signalis interposed in a path for supplying a DC bias to said first switchmeans, and third switch means for switching to resonate with said secondhigh frequency signal by short-circuiting a part of said second stripline is provided in a halfway portion of said second strip line.

The high frequency switch with the above constitution is usable inmultiple frequency bands by controlling conduction of the first switchmeans and switching the second switch means or the third switch means.The switch means may be constituted of a diode, for example.

Thirdly, the invention provides a high frequency switch characterized bycomprising first switch means provided in a transit path of highfrequency signals between a first signal terminal and a second signalterminal to conduct by application of a DC bias, a strip line thatresonates with a first high frequency signal in a predeterminedfrequency band to be supplied to said first signal terminal when saidfirst switch means conducts and is grounded, said strip line connectedbetween said first switch means and said second switch means, a thirdsignal terminal connected between said strip line and said first switchmeans, and second switch means for switching to resonate with a secondhigh frequency signal in the predetermined frequency band by conductingby application of a DC bias to short-circuit a part of said strip line,said second switch means connected in a halfway portion of said stripline.

Fourthly, the invention provides the high frequency switch,characterized in that a second strip line for resonating with said firsthigh frequency signal is interposed in a path for supplying a DC bias tosaid first switch means, and third switch means for switching toresonate with said second high frequency signal by short-circuiting apart of said second strip line is provided in a halfway portion of saidsecond strip line. The high frequency switch with the above constitutionhas a transferable frequency band that can be changed by controllingconduction of the first switch means to switch the transfer path of highfrequency signals and switching the second switch means or the thirdswitch means. The switch means may be constituted of a diode, forexample. Fifthly, this invention provides a high frequency switchcharacterized in that a first strip line and a second strip lineresonating with high frequency signals having different frequencies arecommonly connected to a common signal terminal, in which a first signalterminal and a second signal terminal are connected to the other end ofsaid first and second strip lines, respectively, and first switch meansand second switch means for selectively grounding a connection pointbetween said strip line and the signal terminal are provided.

With the above constitution, the high frequency switch can transfer highfrequency signals in different frequency bands through independentpaths. The switch means may be constituted of a diode, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the configuration of a highfrequency switch according to a first embodiment of the presentinvention.

FIG. 2 is an equivalent circuit diagram of the high frequency switch ofFIG. 1 in which a first switch and a second switch are closed.

FIG. 3 is a circuit diagram showing the configuration of a highfrequency switch according to a second embodiment of the invention.

FIG. 4 is an equivalent circuit diagram of the high frequency switch ofFIG. 1 in which a second switch and a third switch are closed.

FIG. 5 is a circuit diagram showing the configuration of a highfrequency switch according to a third embodiment of the invention.

FIG. 6 is a circuit diagram showing the configuration of a highfrequency switch according to a fourth embodiment of the invention.

FIG. 7 is a circuit diagram showing the configuration of a highfrequency switch according to a fifth embodiment of the invention.

FIG. 8 is a circuit diagram showing the configuration of a highfrequency switch of the prior art.

In these figures, 1 and 107 denote a first signal terminal, 2, 4, 7, 12,22, 32, 38, 42, 52, 102, 106, 202 and 206 denote a capacitor, 3 denotesa first diode, 5 denotes a second signal terminal, 6, 34, 44, 104 and204 denote an inductor, 8 denotes a first switch, 9, 15 and 25 denote aresistor, 10 and 103 denote a first power supply terminal, 11 and 31denote a strip line, 13, 33 and 203 denote a second diode, 14 denotes asecond switch, 16 denotes a second power supply terminal, 21 and 41denote a second strip line, 23 and 36 denote a third diode, 24 denotes athird switch, 26 denotes a third power supply terminal, 30 and 105denote a first control terminal, 35 and 205 denote a second controlterminal, 37 denotes a third signal terminal, 43 denotes a third controlterminal, 44 denotes a fourth switch, 51 denotes a common signalterminal, 101 denotes a first strip line, and 201 denotes a second stripline.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings. In the drawings, thecommon components are designated by the same numerals.

First Embodiment

FIG. 1 is a circuit diagram showing the configuration of a highfrequency switch according to a first embodiment of the presentinvention.

In FIG. 1, a first signal terminal 1 is connected via a capacitor 2 tothe anode of a first diode 3 as switching means, the cathode of thefirst diode 3 being connected via a capacitor 4 to a second signalterminal 5. An inductor 6 is connected to the anode of the first diode3, the other end of this inductor 6 being connected to a capacitor 7 anda first switch 8. And the other end of the capacitor 7 is grounded, andthe other end of the first switch 8 is connected via a resistor 9 to afirst power supply terminal 10.

Also, the cathode of the first diode 3 is connected to a strip line 11having the electrical length L1. A capacitor 12 is connected at aposition with the distance L2 from one end in a halfway portion of thestrip line 11, the other end of the capacitor 12 being connected to theanode of a second diode 13 and a second switch 14 as switch means, andthe cathode of the second diode 13 is grounded. And the other end of thesecond switch 14 is connected via a resistor 15 to a second power supplyterminal 16.

Herein, the capacitor 7 is the bypass capacitor for preventing highfrequency signals from leaking into the first power supply terminal 10,and reducing the impedance at a frequency used for this high frequencyswitch at a terminal of the inductor 6 on the switch 8 side. Also, thecapacitors 2, 4 and 12 are coupling capacitors for cutting the DCcomponents which are inserted to prevent a bias current of the firstdiode 3 and the second diode 13 from flowing into the high frequencycircuit connected to the first and second signal terminals 1 and 5. Eachof these capacitors has a small enough impedance for the high frequencysignal in the frequency band for use.

Also, the inductor 6 has a large enough impedance for the high frequencysignal in the frequency band for use, and prevents high frequencysignals from leaking into the first power supply terminal 10 when thefirst switch 8 is closed. Also, the first and second diodes 3 and 13 usea PIN diode or a band switching diode. And the strip line 11 isconfigured such that the electrical lengths L1 and L2 have the relationof L1=λ1/4, L2=λ2/4 for a first high frequency signal in a frequencyband with the central frequency f1 and the wavelength λ1 and a secondhigh frequency signal in a frequency band with the central frequency f2and the wavelength λ2.

The operation of the high frequency switch according to the firstembodiment of the invention will be described below.

First of all, when the first switch 8 is opened, the first diode 3 is ina cut-off state, because no bias current flows from the first powersupply terminal 10. Accordingly, the high frequency signal is nottransferred between the first signal terminal 1 and the second signalterminal 5.

Then, when the first switch 8 is closed, a bias current flows in a pathfrom the first power supply terminal 10 to the resistor 9, the inductor6, the first diode 3 and the strip line 11. Thereby, the first diode 3is conducting in the forward direction bias, so that the high frequencysignal can be transferred between the first signal terminal 1 and thesecond signal terminal 5.

At this time, if the second switch 14 is open, the second diode 13 is ina cut-off state because no current flows from the second power supplyterminal 16, whereby a circuit containing the capacitor 12 and thesecond diode 13 is equivalently ignored. Accordingly, the strip line 11is grounded with the electrical length L1, and resonates with a firsthigh frequency signal with frequency f1 and wavelength λ1, so that theimpedance as seen from the first diode 3 becomes infinite. However, itdoes not resonate with a second high frequency signal with frequency f2and wavelength λ2, so that the impedance as seen from the first diode 3becomes small. Thereby, the first high frequency signal can be onlytransferred between the first signal terminal 1 and the second signalterminal 5.

On the other hand, if the second switch 14 is closed, a forward biascurrent flows from the power supply terminal 16 via the resistor 15 tothe second diode 13, so that the second diode 13 conducts. Accordingly,for the high frequency signal, the strip line 11 is equivalent to thatgrounded with the electrical length L2 via the capacitor 12 and thesecond diode 13.

In an equivalent circuit of FIG. 2, the strip line 11 is grounded withthe electrical length L2, and resonates with a second high frequencysignal with frequency f2 and wavelength λ2, so that the impedance asseen from the anode of the first diode 3 becomes infinite. Thereby, thesecond high frequency signal can be only transferred between the firstsignal terminal 1 and the second signal terminal 5.

In this manner, with the first embodiment of the invention, conductionof the first diode 3 is controlled by opening or closing the firstswitch 8, and the transferable frequency band between the first signalterminal 1 and the second signal terminal 5 can be changed by switchingthe second switch 14, whereby this high frequency switch is usable inmultiple frequency bands. If both the frequency bands are selected to becloser, the transferable frequency bands become almost continuous,thereby enabling the high frequency switch to operate in a wider band.

In the first embodiment, one frequency switching circuit consisting ofthe second diode 13 and the second switch 14 is provided to switchbetween two frequency bands. However, the strip line 11 is provided witha plurality of branches, for which corresponding switching circuits areprovided, whereby the high frequency switch is usable in multiple bandsor wider band.

Also, electric currents from the first and second power supply terminal10 and 16 are controlled by opening or closing the first switch 8 andthe second switch 14, respectively, but may be controlled by a controlsignal for outputting a specific waveform.

Second Embodiment

FIG. 3 is a circuit diagram showing the configuration of a highfrequency switch according to a second embodiment of the invention. Astrip line having the electrical length changeable is provided, insteadof the inductor 6 in the configuration of the first embodiment ofFIG. 1. The same parts are designated by the same numerals as in FIG. 1.In FIG. 3, a second strip line 21 having the same electrical length L1as the strip line 11 is connected to the anode of a first diode 3, theother end of the second strip line 21 being connected to one end of thecapacitor 7 and the first switch 8. A capacitor 22 is connected at aposition with the distance L2 from one end in a halfway portion of thesecond strip line 21, the other end of the capacitor 22 being connectedto the anode of a third diode 23 and a third switch 24 as switch means,and the cathode of the third diode 23 is grounded. Moreover, the otherend of the third switch 24 is connected via a resistor 25 to a thirdpower supply terminal 26.

Herein, the capacitor 22 is the coupling capacitor for cutting the DCcomponents, which is inserted to prevent a bias current from flowing viathe third diode 23, and has a small enough impedance for the highfrequency signal in the frequency band for use.

The operation of the high frequency switch according to the secondembodiment of the invention will be described below.

First of all, when the first switch 8 is opened, the high frequencysignal is not transferred between the first signal terminal 1 and thesecond signal terminal 5, because no bias current flows from the firstpower supply terminal 10 to the first diode 3, as in the firstembodiment. Then, when the first switch 8 is closed, a bias currentflows in a path from the first power supply terminal 10 to the resistor9, the second strip line 21, the first diode 3 and the strip line 11.Thereby, the first diode 3 is conducting in the forward direction bias,so that the high frequency signal can be transferred between the firstsignal terminal 1 and the second signal terminal 5.

In this state, if the second switch 14 is open, the strip line 11resonates with a first high frequency signal with frequency f1 andwavelength λ1, as described in the first embodiment, so that theimpedance as seen from the first diode 3 becomes infinite.

At the same time, if the third switch 24 is open, the third diode 23 isin the cut-off state, because no current flows from the third powersupply terminal 26, whereby a circuit containing the capacitor 22 andthe third diode 23 is equivalently ignored. Accordingly, for the highfrequency signal, the second strip line 21 is equivalent to thatgrounded with the electrical length L2 via the capacitor 12, andresonates with a first high frequency signal with frequency f1 andwavelength λ1, like the strip line 11, so that the impedance as seenfrom the cathode of the first diode 3 becomes infinite. Thereby, thefirst high frequency signal can be only transferred between the firstsignal terminal 1 and the second signal terminal 5.

On the other hand, if the second switch 14 is closed, the strip line 11resonates with a second high frequency signal with frequency f2 andwavelength λ2, so that the impedance as seen from the anode of the firstdiode 3 becomes infinite, as described in the first embodiment.

At this time, if the third switch 24 is closed, a forward bias currentflows through the third diode 23 from the third power supply terminal 26via the resistor 25, so that the third diode 23 conducts. Accordingly,the second strip line 21 is equivalently grounded with the electricallength L2 via the capacitor 22 and the third diode 23 as shown in anequivalent circuit of FIG. 4.

In the equivalent circuit of FIG. 4, the second strip line 21 groundedwith the electrical length L2 resonates with a second high frequencysignal with frequency f2 and wavelength λ2, so that the impedance asseen from the anode of the first diode 3 becomes infinite. Thereby, thesecond high frequency signal can be only transferred between the firstsignal terminal 1 and the second signal terminal 5.

In this manner, with the second embodiment of the invention, conductionof the first diode 3 is controlled by opening or closing the firstswitch 8, and the transferable frequency band between the first signalterminal 1 and the second signal terminal 5 can be changed by switchingthe second switch 14 and the third switch 24 at the same time, wherebythis high frequency switch is usable in multiple frequency bands.

The second embodiment has the same effect as the first embodiment.Furthermore, the second strip line 21 resonating with any of the firstand second high frequency signals and having the infinite impedance isemployed in the path for supplying bias current to the first diode 3,whereby there is a specific effect of the second embodiment that thetransmission loss of high frequency signals is quite smaller than in thefirst embodiment using the inductor 6 of FIG. 1.

Third Embodiment

FIG. 5 is a circuit diagram showing the configuration of a highfrequency switch according to a third embodiment of the invention. Thesame parts are designated by the same numerals as in FIG. 1, and thedescription for those parts is omitted.

In FIG. 5, a first signal terminal 1 is connected via a capacitor 2 tothe anode of a first diode 3 as switching means. An inductor 6 isconnected to the anode of the first diode 3, the other end of thisinductor 6 being connected to the capacitor 8 with one end connected toa first control terminal 30.

A third signal terminal 37 is connected via a capacitor 38 to thecathode of the first diode 3, which is then connected to a strip line 31with the electrical length L1. A capacitor 32 is connected at a positionwith the distance L2 from one end in a halfway portion of the strip line31, the other end of the capacitor 32 being connected to the anode of asecond diode 33 and an inductor 34 as switch means. Moreover, thecathode of the second diode 33 is grounded, and the other end of theinductor 34 is connected to a second control terminal 35. Also, theother end of the strip line 31 is connected to a third diode 36 with oneend grounded and the capacitor 11, the other end of which is connectedto the second signal terminal 5.

Herein, the capacitors 32 and 38 are the coupling capacitors for cuttingthe DC components, the capacitor 32 being inserted to prevent a biascurrent of the second diode 33 from flowing into the strip line 31, andthe capacitor 38 being inserted to prevent bias current of the firstdiode 3 from leaking into the first signal terminal 37. Each of thesecapacitors has a small enough impedance for the high frequency signal inthe frequency band for use.

Also, the inductor 34 has a large enough impedance for the highfrequency signal in the frequency band for use, and prevents highfrequency signals transferred to the strip line 31 from leaking into thesecond control terminal 35.

The operation of the high frequency switch according to the thirdembodiment of the invention will be described below.

First of all, if a positive voltage is applied to the first controlterminal 30, a bias current flows in a path from the inductor 6 throughthe first diode 3 and the strip line 31 to the third diode 36. At thistime, if no positive voltage is applied to the second control terminal35, the second diode 33 has no current flowing and is in the cut-offstate, whereby a circuit containing the capacitor 32 and the seconddiode 33 is equivalently ignored. Accordingly, the strip line 31 isgrounded with the electrical length L1 via the third diode 36, andresonates with a first high frequency signal with frequency f1 andwavelength λ1, so that the impedance as seen from the first diode 3becomes infinite. However, it does not resonate with a second highfrequency signal with frequency f2 and wavelength λ2, so that theimpedance as seen from the anode of the first diode 3 becomes small.Thereby, the first high frequency signal can be only transferred betweenthe first signal terminal 1 and the third signal terminal 37.

On the other hand, if a positive voltage is applied to the first controlterminal 30, and a positive voltage is applied to the second controlterminal 35 at the same time, the second diode 33 has a forward biascurrent flowing via the inductor 34 and conducts. Accordingly, for thehigh frequency signal, the strip line 31 is equivalent to that groundedwith the electrical length L2 via the capacitor 32 and the second diode33. Thus, the strip line 31 resonates with a second high frequencysignal with frequency f2, so that the impedance as seen from the anodeof the first diode 3 becomes infinite. Thereby, the second highfrequency signal can be only transferred between the first signalterminal 1 and the third signal terminal 37. If no positive voltage isapplied to the first control terminal 30, no bias current flows throughthe first diode 3 and the third diode 36. Accordingly, no high frequencysignal is transferred between the first signal terminal 1 and the thirdsignal terminal 37, and between the first signal terminal 1 and thesecond signal terminal 5. At this time, if no positive voltage isapplied to the second control terminal 35, the second diode 33 has nocurrent flowing and is in the cut-off state, whereby a circuitcontaining the capacitor 32 and the second diode 33 is equivalentlyignored.

Thereby, both the first and second high frequency signals can betransferred between the second signal terminal 5 and the third signalterminal 37.

In this manner, with the third embodiment of the invention, thetransferable path of high frequency signals can be switched between thefirst signal terminal 1 and the third signal terminal 37, or between thesecond signal terminal 5 and the third signal terminal 37 by controllingthe voltage applied to the first control terminal 30. Also, when apositive voltage is applied to the first control terminal 30, thetransferable frequency band between the first signal terminal 1 and thethird signal terminal 37 can be changed, depending on whether or not thepositive voltage is applied to the second control terminal 35, wherebythis high frequency switch is usable in multiple frequency bands.

This reduces the transferring loss as compared with the conventionalhigh frequency switch prepared for every frequency band, because theswitches for transferring the high frequency signal can be less. Thesignal is only transferred through the diode 3 among the diodes causingdistortion, whereby the harmonic distortion is favorable.

Further, with the third embodiment of the invention, like the first andsecond embodiments, the high frequency switch is usable in the wide areaby selecting two frequency bands closely. It is clear that themulti-band or wide band is allowed by providing plural branches andcircuits on the strip line 31.

In a circuit of FIG. 5, if the first signal terminal 1 is connected to asending circuit, the second signal terminal 2 is connected to areceiving circuit, and the third signal terminal 37 is connected to theantenna, the high frequency switch for switching one antenna between thesending and receiving circuits can be constituted, resulting in asimplified circuit configuration of the mobile communication device.

Fourth Embodiment

FIG. 6 is a circuit diagram showing the configuration of a highfrequency switch according to a fourth embodiment of the invention. Astrip line having the electrical length changeable is provided, insteadof the inductor 6 in the configuration of the third embodiment of FIG.5. The same parts are designated by the same numerals as in FIG. 5, andthe description of those parts is omitted.

In FIG. 6, a second strip line 41 having the same electrical length L1as the strip line 31 has its one end connected to the anode of the firstdiode 3 as switch means, the other end of the second strip line 41 beingconnected to the capacitor 7 and the first control terminal 30. Acapacitor 42 is connected at a position with the distance L2 from oneend in a halfway portion of the second strip line 41, the other end ofthe capacitor 42 being connected to the anode of a fourth diode 43 andan inductor 44 as switch means. Moreover, the other end of the inductor44 is connected to a third control terminal 45 and the cathode of thefourth diode 43 is grounded.

Herein, the capacitor 42 is the coupling capacitor for cutting the DCcomponents, which is inserted to prevent a bias current from not flowingvia the second strip line 41 and the fourth diode 43 into the firstdiode 3, when a positive voltage is applied to the first controlterminal 30, and has a small enough impedance for the high frequencysignal in the frequency band for use.

Also, the inductor 44 has a large enough impedance for the highfrequency signal in the frequency band for use, and prevents highfrequency signals from leaking into the third control terminal 45.

The operation of the high frequency switch according to the fourthembodiment of the invention will be described below.

First of all, if a positive voltage is applied to the first controlterminal 30, a bias current flows in a path from the second strip line41 through the first diode 3 and the strip line 31 to the third diode36. Then, the high frequency signal can be transferred between the firstsignal terminal 1 and the third signal terminal 37, as in the thirdembodiment. Furthermore, if no positive voltage is applied to the secondcontrol terminal 35, a circuit containing the capacitor 32 connected tothe strip line 31 and the second diode 33 is equivalently ignored as inthe third embodiment. At the same time, if no positive voltage isapplied to the third control terminal 45, a circuit containing thecapacitor 42 and the fourth diode 43 is also equivalently ignored.

Accordingly, the strip line 31 and the second strip line 41 are groundedwith the electrical length L1 via the third diode 36 and the capacitor7, respectively, and resonates with a first high frequency signal withfrequency f1 and wavelength λ1, so that the impedance as seen from thefirst diode 3 becomes infinite. Thereby, the first high frequency signalcan be only transferred between the first signal terminal 1 and thethird signal terminal 37.

On the other hand, if a positive voltage is applied to the first controlterminal 30, and a positive voltage is applied to both the secondcontrol terminal 35 and the third control terminal 37 at the same time,a forward bias current flows through the second diode 33 and the fourthdiode 43, whereby the strip line 31 and the second strip line 41 areequivalently grounded with the electrical length L2. Thus, the stripline 31 and the second strip line 41 resonate with a second highfrequency signal with frequency f2, whereby the second high frequencysignal can be only transferred between the first signal terminal 1 andthe third signal terminal 37.

If no positive voltage is applied to the first control terminal 30, nohigh frequency signal is transferred between the first signal terminal 1and the third signal terminal 37, and between the first signal terminal1 and the second signal terminal 5 as in the third embodiment. At thistime, if no positive voltage is applied to the second control terminal35, both the first and second high frequency signals can be transferredbetween the second signal terminal 5 and the third signal terminal 37 asin the third embodiment.

In this manner, with the fourth embodiment of the invention, thetransferable path of high frequency signals can be switched between thefirst signal terminal 1 and the third signal terminal 37, or between thesecond signal terminal 5 and the third signal terminal 37 by controllingthe voltage applied to the first control terminal 30 as in the thirdembodiment.

This fourth embodiment is functionally identical to the third embodimentas previously described, and has the same features. Moreover, thespecific features of the fourth embodiment include the following. Thatis, when a positive voltage is applied to the first control terminal 30to enable the high frequency signal to be transferred between the firstsignal terminal 1 and the third signal terminal 37, the strip line 31and the second strip line 41 have the electrical length changed toresonate in the frequency band used by controlling the voltage appliedto the second control terminal 35 and the third control terminal 45 atthe same time, whereby the transferring loss of the high frequencyswitch can be quite reduced.

Fifth Embodiment

FIG. 7 is a circuit diagram showing the configuration of a highfrequency switch according to a fifth embodiment of the invention.

In FIG. 7, a capacitor 52 is connected to a common signal terminal 51,and a fist strip line 101 and a second strip line 201 are connected tothe other end of the capacitor 52.

A capacitor 102 is connected to the first strip line 51, and a firstdiode 103 and an inductor 104 as switching means are connected to theother end of this capacitor 012. And the other end of the first diode103 is grounded, the other end of the inductor 104 being connected to afirst control terminal 105. Also, a capacitor 106 is connected to theother end of the first strip line 101, the other end of the capacitor106 being connected to a first signal terminal 107.

On the other hand, the second strip line 201, which has the sameconfiguration as above, is connected to a capacitor 202, a second diode203 as switching means, an inductor 204, and a second control terminal205, and connected to a capacitor 206, the other end of the capacitor206 being connected to a second signal terminal 207.

Herein, the first strip line 101 is configured such that the electricallength L2 has the relation of L2=λ2/4 for a second high frequency signalin a frequency band with the central frequency f2 and the wavelength λ2.Also, the second strip line 201 is configured such that the electricallength L1 has the relation of L1=λ1/4 for a first high frequency signalin a frequency band with the central frequency f1 and the wavelength λ1.

Moreover, the capacitors 52, 102, 106, 202 and 206 are couplingcapacitors for cutting the DC components which are inserted to prevent abias current from the control terminals 105 and 205 from flowing intothe high frequency circuit connected to the signal terminals 51, 107 and207. Each of these capacitors has a small enough impedance for the highfrequency signal in the frequency band for use.

The operation of the high frequency switch according to the fifthembodiment of the invention will be described below.

First of all, when no voltage is applied to the first control terminal105, the first diode 103 is in the cut-off state, because no currentflows through the first diode 103. Hence, a circuit containing thecapacitor 102 and the second diode 103 is equivalently ignored. Thecommon signal terminal 51 and the first signal terminal 107 conduct toenable the high frequency signal to be transferred.

Then, if a positive voltage is applied to the second control terminal205, a bias current flows via the inductor 205 and the second diode 203,whereby the second strip line 201 is equivalently grounded with theelectrical length L1, and resonates with a first high frequency signalwith frequency f1 and wavelength λ1, so that the impedance as seen fromthe connection point A becomes infinite. Thereby, the first highfrequency signal can be only transferred between the common signalterminal 51 and the first signal terminal 107.

On the other hand, if a positive voltage is applied to the first controlterminal 105 and no voltage is applied to the second control terminal206, the first strip line 101 in complementary relation is equivalentlygrounded with the electrical length L2, and resonates with a second highfrequency signal with frequency f2 and wavelength λ2, so that theimpedance as seen from the connection point A becomes infinite. Thereby,the second high frequency signal can be only transferred between thecommon signal terminal 51 and the second signal terminal 207.

In this manner, with the fifth embodiment of the invention, the highfrequency switch is constituted in which the first and second highfrequency signals in different frequency bands are transferred throughindependent paths by controlling the voltage applied to the firstcontrol terminal 105 and the second control terminal 205. Because nodiode is employed in the transmission path of the high frequency signal,there is the effect that the loss cause by the high frequency signal oflarge power being transferred through the diode is minimized, and theharmonic distortion characteristic is favorable.

Moreover, in a circuit of FIG. 7, if the common signal terminal 51 isconnected to the antenna, the first signal terminal 107 is connected toa sending circuit, and the second signal terminal 207 is connected to areceiving circuit, the high frequency switch is constituted of a simplecircuit in which one antenna is easily switched and commonly usedbetween the sending and receiving circuits of different frequency bands,can be constituted.

In the fifth embodiment as above described, the electrical length of thestrip line constituting the high frequency switch is changed bycontrolling the supply of bias current, whereby the high frequencyswitch is usable in multiple frequency bands or wide band.

Also, the transferable path of high frequency signals is switched bycontrolling the voltage applied to the control terminal, and theelectrical length of the strip line is changed, whereby the highfrequency switch capable of transferring the high frequency signal inmultiple frequency bands is provided.

Moreover, a plurality of transferring paths of high frequency signalsare provided, and the voltage applied to the control terminal iscontrolled, whereby the high frequency switch capable of transferringthe high frequency signal in different frequency bands throughindependent paths is provided.

The present invention has been described in detail with reference to thespecific embodiments, but it will be apparent to those skilled in theart that various modifications or variations may be made withoutdeparting from the scope or spirit of the invention.

This application is based on JP-A-2001-279762, filed on Sep. 14, 2001,its contents being incorporated herein by reference.

INDUSTRIAL APPLICABILITY

As above described, there is the effect that the high frequency switchcapable of dealing with multiple frequency bands is provided withoutmaking the circuit scale larger by providing a plurality of switchcircuits.

1. A high frequency switch, comprising: a first switch that is providedin a transmit path of high frequency signals between a first signalterminal and a second signal terminal, and conducts based on applicationof a DC bias; a strip line that resonates with a first high frequencysignal in a predetermined frequency band which is supplied to said firstsignal terminal when said first switch conducts, wherein the strip lineis grounded and is connected between said first switch and said secondsignal terminal; a third signal terminal that is connected between saidstrip line and said first switch; and a second switch that switches soas to resonate the strip line with a second high frequency signal in apredetermined frequency band by conducting based on application of a DCbias to short-circuit a part of said strip line, said second switchconnected in a halfway portion of said strip line.
 2. The high frequencyswitch according to claim 1, wherein a second strip line for resonatingwith said first high frequency signal is interposed in a path forsupplying a DC bias to said first switch, and wherein a third switch,that switches so as to resonate said second strip line with said secondhigh frequency signal by short-circuiting a part of said second stripline so as to be grounded, is provided in a halfway portion of saidsecond strip line.